DISTRIBUTION OF ANNEXIN-I, ANNEXIN-II, AND ANNEXIN-IV IN BOVINE MAMMARY-GLAND

Annexins belong to a family of proteins that are characterized by thei r ability to bind phospholipids in a Ca2+-dependent manner that is tho ught to be involved in a variety of biological processes. The present study determined the localization of annexins in subcellular fractions , nuclei in particular, of cow mammary gland by immunoblot analysis us ing monoclonal antibodies to annexins I, II, TV, and VI. The analysis revealed that annexins I, II, and IV were present in cytosol, but VI w as not. Annexins I and IV were found in the nuclear fraction, but anne xin II was only faintly present. Annexin VI was also undetectable in t his fraction. Cytosolic annexin I had a molecular mass of 36 kDa. The 36-kDa annexin I was also found in the nuclear fraction. A 38-kDa anne xin I was additionally detected in nuclei. The cytosolic and nuclear 3 6-kDa annexin I and the nuclear 38-kDa annexin I showed different isoe lectric points, as revealed by two-dimensional PAGE. Annexin TV from c ytosolic and nuclear fractions had similar molecular masses and isoele ctric points.